1. Field of the Invention
This invention relates to a method of producing a one-part silicone reinforced sealant which is stable in the absence of moisture, but cures to an elastomer upon exposure to moisture.
2. Background Information
A method of economically producing a reinforced one-part silicone sealant which was stable in the absence of moisture, but cured to an elastomer in the presence of moisture was desired. Experience with the type of sealant based upon hydroxyl or alkoxy functional polydiorganosiloxane, alkoxy functional crosslinker, and titanate catalyst revealed that such sealants suffered in that as they shelf aged, they gradually lost the ability to cure upon exposure to moisture.
A method was developed to make a sealant composition which had the desired physical properties when cured and which had improved storage stability upon storage in the absence of moisture.
Although there was no known published art which suggested how to solve the problem of loss of cure upon storage of this type of silicone sealant, once the cause of the problem was discovered other prior art became of interest.
U.S. Pat. No. 3,122,522, issued Feb. 25, 1964 to Brown and Hyde discloses a siloxane composition, each molecule of which consists essentially of (1) at least two units of the formula EQU [R'(OCH.sub.2 CH.sub.2 ).sub.c O].sub.a (R.sub.b)SiZ(R.sub.2)SiO.sub.0.5
and units of the formula ##EQU1## where each a has a value ranging from 2 to 3, each b has a value ranging from 0 to 1, the sum of a and b in any unit (1) is no greater than 3, each c has a value ranging from 1 to 2, each d has a value ranging from 0 to 2, and Z is a divalent hydrocarbon radical of from 2 to 18 inclusive carbon atoms, Z being free of aliphatic unsaturation. Each molecule of the silicone composition has an average of from 1.3 to 2 R groups per silicon atom and there are at least 7 units of ##EQU2## per molecule.
U.S. Pat. No. 3,175,993, issued March 30, 1965 to Weyenberg discloses a composition consisting essentially of the average formula ##STR1## in which each R is free of aliphatic unsaturation, Z is a divalent hydrocarbon radical free of aliphatic unsaturation, y has a value of from 0 to 2 inclusive, x has a value of at least 3, and a has an average value from 2 to 3 inclusive.
Both of the above references teach preparation of the siloxane by reacting siloxanes containing --SiH groups with the appropriate silane containing a monovalent hydrocarbon radical containing an aliphatic or cycloaliphatic group in the presence of a platinum catalyst through the reaction of the --SiH and aliphatic C.dbd.C group. This reaction produces the divalent Z radical. Alternatively, the C.dbd.C group can be on the siloxane and the --SiH can be on the silane.
European Patent Application 123 935 A , published Nov. 7, 1984 by Toten and Pines, discloses an alkoxysilyl functional silicone including at least one functional group of the formula ##STR2## where w is an integer of from 2 to about 20, useful as capable of imparting satisfactory lubricity and other properties such as softness to a variety of textile fabrics.
European Patent Application 0110251, published June 6, 1984, discloses a process for producing alkoxy-terminated polysiloxanes useful to produce room temperature vulcanizing silicone rubber compositions. The process anhydrously reacts a silanol or vinyl siloxane with a polyalkoxy crosslinking agent which is an alkoxy silane in the presence of a platinum catalyst. This alkoxy-terminated polysiloxane can also be mixed with treated filler and condensation catalyst. This application teaches that an alkoxy-terminated polysiloxane having no silethylene linkage at the polymer terminal silicon is equivalent to a polydiorganosiloxane that does contain a trialkoxysilethylene terminal group.
There are many patents directed to the system of producing silicone sealants based upon the use of alkoxy functional polymers, alkoxy functional crosslinkers, and titanate catalysts. Representative of these is U.S. Pat. No. 3,334,067, issued Aug. 1, 1967, to Weyenberg. Weyenberg discloses a method of making one component room temperature curing siloxane rubber. His compositions are stable in the absence of moisture, but cure upon exposure to moisture. The method comprises mixing in the absence of moisture a hydroxyl endblocked siloxane polymer, a silane of the formula R'Si(OR").sub.3 and a beta-dicarbonyl titanium compound.
In U.S. Pat. No. 3,383,355, issued May 14, 1968, Cooper discloses polymers having alkoxy groups bonded to terminal silicon atoms by reacting a hydroxylated organosiloxane polymer with an alkoxy silane in the presence of a suitable catalyst. He discloses that such functional diorganopolysiloxanes having from two to three alkoxy radicals attached to each terminal silicon atom are curable in the presence of moisture and a suitable hydrolysis and condensation catalyst to a rubbery material.
Smith et al., in U.S. Pat. No. 3,856,839, issued Dec. 24, 1974, disclose alkanedioxy titanium chelates which catalyze the cure of a composition which also contains methyltrimethoxysilane and a silanol chain-stopped polydiorganosiloxane fluid. The particular chelated titanium compound is stated to be desirable because it does not cause thickening during the manufacture of the composition as does the previously known titanium compounds.
None of the disclosures in this background information is of any assistance in solving the problem of how to improve the shelf life of silicone sealants that lose the ability to cure upon long time storage in the absence of moisture, said sealants being catalyzed with titanium compounds.